1. Field of the Invention
This invention relates to a faulty wiring detection device for an air conditioner, which improves the safety of an air conditioner by preventing faulty wiring to a power supply to be connected with the air conditioner.
2. Description of the Related Art
FIG. 11 is a diagram illustrating normal wiring between a conventional air conditioner and a power supply, where denoted 1 is a primary power supply that provides a single-phase alternating current, 2 a ground resistance existing between an N-phase of the primary power supply and a ground, 3 a ground point, 4 wiring from the primary power supply, 5 a wall socket for the air conditioner, 6 a plug of the air conditioner, 7 a power cord of the air conditioner, 8 an indoor unit of the air conditioner, 9 a power supply terminal block of the indoor unit 8, 10 a control board of the indoor unit 8, 11 power supply wiring from the indoor unit 8 to an outdoor unit 12 of the air conditioner, 12 the outdoor unit of the air conditioner, 13 a power supply terminal block of the outdoor unit 12, and 14 a control board of the outdoor unit 12.
FIG. 12 is an example of a wiring diagram showing faulty wiring of the power supply in a conventional air conditioner. Similar components shown in FIG. 12 have the same symbols as in FIG. 11, and their descriptions are not repeated. Denoted 15 is an insulation resistance between the ground point 3 and a ground terminal E of the power supply terminal block 13 of the outdoor unit 12.
Referring now to FIG. 12, the operation of the air conditioner is described for the case in which it has faulty wiring in the power lines.
As a first example of faulty wiring, if the L-phase of the primary power supply 1 is improperly coupled with the ground terminal E of the wall socket 5 for the air conditioner, then the source voltage is directly applied to the ground terminals E of the indoor unit 8 and the outdoor unit 12. The housing of the outdoor unit 12 and the piping are connected to the terminals E of the power supply terminal block 9 of the indoor unit 8 and the power supply terminal block 13 of the outdoor unit 12. Thus, current i=V/R(A) runs that is determined by an insulation resistance R between the terminal E and the ground point 3 (where V is the source voltage of the primary power supply 1). In this case, unless a ground-fault circuit interrupter or an automatic overcurrent breaker is installed between the primary power supply 1 and the wall socket 5 for the air conditioner, a current larger than the tolerance runs in the power cord 7 of the air conditioner and causes heat generation in the cord, leading to a dangerous condition, if this insulation resistance R falls for any reason. Al this moment, the air conditioner is not activated because there is no sufficient voltage applied for operation between the L-phase and N-phase on the power supply terminal blocks 9 and 13 of the air conditioner.
FIG. 13 shows a second example of a wiring diagram showing faulty wiring of the power supply in the conventional air conditioner. Since the N-phase of the primary power supply 1 is coupled with the ground terminal E of the wall socket 5 for the air conditioner, the voltage applied between the N-phase and the terminal E is also applied to the metallic portions of the air conditioner such as the housings of the indoor unit 8 and the outdoor unit 12 and the piping. At this moment, a current i, which is determined by the sum of resistances (r+R) xcexa9 (ohm), namely, the ground resistance r of the N-phase of the primary power supply 1 and the ground resistance R of the outdoor unit 12, runs in the ground line E. If an automatic overcurrent breaker for cutting wiring executed by an excessive current larger than a rated current for wiring is installed between the-primary power supply 1 and the wall socket 5 for the air conditioner, this flow of current i may cause a dangerous situation.
The air conditioner may operate normally because current runs in the indoor unit 8 and the outdoor unit 12, as shown in FIG. 13, from the L-phase to the ground line E of the primary power supply 1 via the N-phase of the wall socket 5, the N-phase of the power supply terminal block 9 of the indoor unit 8, the N-phase of the power supply terminal block 13 of the outdoor unit 12, the control board 14 of the outdoor unit 12, the L-phase of the power supply terminal block 13 of the outdoor block 12, the L-phase of the power supply terminal block 9 of the indoor unit 8, and the L-phase of the wall socket 5, and the voltage of the primary power supply is applied to the control boards 10, 14 of the indoor unit 8 and the outdoor unit 12. The air conditioner thus appears to work properly despite the faulty wiring if the ground resistance R is large. However, if the ground resistance becomes small for any reason, a large current beyond the tolerance runs in the ground line E and may cause heat generation in the wiring.
In the conventional air conditioners of the above configuration, it is necessary to check for the presence/absence of faulty wiring in the indoor power lines during installation. However, this check is not always performed during the installation of an air conditioner. Moreover, at this moment, even if an automatic overcurrent breaker is installed at a proper position to protect wiring and appliances from overheating caused by overcurrent and short circuit, there may be such problems as overheating due to overcurrent caused by the faulty wiring, unless a proper shut-off current is set in the automatic overcurrent breaker against the rated current for the wiring.
This invention has been made to solve those problems, and an object thereof is to provide such a faulty wiring detection device for an air conditioner that has a simple structure and does not affect the operation of the air conditioner itself. Also this device can detect faulty wiring to the source line of the primary power supply, if any, during installation of an air conditioner, and can notice the user of the presence/absence of faulty wiring through visual, alarm and other means. In addition, this device can prevent problems such as overheating of the circuit due to faulty wiring by shutting off the power lines of the air conditioner.
The faulty wiring detection device according to the present invention is a device for detecting faulty wiring of an air conditioner which is powered by a single-phase two-wire system, a single-phase three-wire system, or a single-phase lower voltage of a three-phase four-wire system, the device comprising: electric signal detection means for detecting an electric signal in between a ground line, a neutral line of the power supply system or one of power lines (hereafter, referred to as xe2x80x9cN-phasexe2x80x9d) of a 200V single-phase three-wire system and a ground line (hereafter, referred to as xe2x80x9cExe2x80x9d), and between a power line or the other power line (hereafter, referred to as xe2x80x9cL-phasexe2x80x9d) with respect to the N-phase power line of the 200V single-phase three-wire system and E; determination means for determining the presence/absence of faulty wiring in the power lines connected to the aforementioned power supply terminal block based on the electric signal provided by the electric signal detection means; and output means for driving a display or alarm means that shows a determination result provided by the determination means.
The electric signal detection means comprises photo-couplers each connected between the L-phase and E and between the N-phase and E.
The electric signal detection means comprises resistors each connected between the L-phase and E and between the N-phase and E.
The electric signal detection means comprises capacitors each connected between the L-phase and E and between the N-phase and E.
Further, there is provided shut-off means for shutting off the electric signal detection means from the N-phase and L-phase based on a signal provided by the output means when the determination means has detected faulty wiring.
There is also provided shut-off means for shutting off the power lines connected to the air conditioner based on a signal provided by the output means when the determination means has detected faulty wiring.
There is also provided shut-off means for shutting off the power lines of a peripheral external device of-the air conditioner based on a signal provided by said output means when the determination means has detected faulty wiring.